A computing system may use an interface to connect to one or more peripheral devices, such as data storage devices, printers, scanners and the like. The interface typically includes a data communication bus that attaches and allows orderly communication among the devices and the computing system. A system may include one or more communication buses. In many systems a logic chip, known as a bus controller, monitors and manages data transmission between the computing system and the peripheral devices by prioritizing the order and the manner of device control and access to the communication buses. Control rules, also known as communication protocols, are imposed to promote the communication of information between computing systems and peripheral devices. For example, Small Computer System Interface (SCSI) is an interface, widely used in computing systems, such as desktop and mainframe computers, that enables connection of multiple peripheral devices to a computing system.
SCSI is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners, and optical drives (CD, DVD, etc.). The SCSI standard contains definitions of command sets of specific peripheral device types; the presence of “unknown” as one of these types means that in theory it can be used to interface almost any device, but the standard is highly pragmatic and addressed toward commercial requirements.
In computer hardware, Serial Attached SCSI (SAS) is a computer bus technology primarily designed for transfer of data to and from devices such as hard drives, CD-ROM drives and so on. SAS is a serial communication protocol for direct attached storage (DAS) devices. It is designed as a replacement for parallel SCSI, allowing for much higher speed data transfers than previously available, and is backwards-compatible with Serial Advanced Technology Attachment (SATA drives). Though SAS uses serial communication instead of the parallel method found in traditional SCSI devices, it still uses SCSI commands for interacting with SAS end devices. SAS protocol is developed and maintained by T10, a technical committee of the International Committee for Information Technology Standards (INCITS). The current draft revision of the SAS protocol can be found in the Working Draft—American National Standard: Project T10/1760-D, Revision 5a, Jul. 21, 2006, and is incorporated herein by reference.